GB2379185A

GB2379185A - Implant forming method

Info

Publication number: GB2379185A
Application number: GB0220208A
Authority: GB
Inventors: Keita Abe; Shingo Shiotani; Motomasa Kato; Takamitsu Yoshida
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 2001-08-30
Filing date: 2002-08-30
Publication date: 2003-03-05
Anticipated expiration: 2022-08-30
Also published as: JP2004057355A; DE10240157A1; US20040138591A1; US20030042641A1; GB0220208D0; US7113841B2; FR2843537A1; JP4083492B2; JP4060063B2; US7050877B2; DE10334122A1; GB2379185B; FR2829017A1; JP2003153925A; FR2843537B1; JP2003070816A

Abstract

An implant designing method to be applied to a body of bone (100) which has a portion of bone missing (101), wherein the bone body is substantially symmetric with respect to a plane of symmetry (102). The method comprises generating three-dimensional data of the bone based on a plurality of pieces of tomographic data of the bone, and estimating a shape of the bone (101) which should exist at the missing portion, using part (103) of the three-dimensional data corresponding to a symmetrical part of the missing portion. A method of forming the implant is also disclosed.

Description

l IMPLANT FORMING METHOD

The present invention relates to z method for forming a three-dimensional implant.

5 Conventionally, when a body of bone, for example bones of a skull, cheek bone, jaw bone or the like are partially lost, implants made of artificial material are implanted in the deficient part, and fixed thereat (reconstruction of deficient portion of bone).

10 In the conventional art of reconstruction of the deficient bone, the material and shape of the implant is very important. Regarding the material, ceramics which have excellent biocompatibility are widely used.

15 Regarding the shape, the implant is conventionally formed as follows.

Firstly, using CT (Computer Tomography) data of the body of bone having the deficient portion, a model corresponding to the body of bone is formed using wood or the like. Then, in the 20 deficient portion of the model, paper-mache pulp or the like is filled in the deficient portion of the model to obtain a shape of an implant (i.e., the shape of body of bone to be located at the deficient portion).

When the shape of the implant is determined in sue:. a 25 manner, however, sufficient reproductivity cannot be obtained.

For example' bones of the skull are typically reproduced as a continuum of smooth spheres. However, the bones of the skull are not usually a continuum o smooth spheres, and the curvatures are different at various points.''herefore, an implant which is 5 formed as a continuum of smooth spheres has less reproductivity.

Regarding the cheek bone or jaw bone, it is more difficult to achieve the high reproductivity.

In another case, the shape of an implant is determined as follows.

10 Firstly, CT images are obtained with respect to a plurality of cross sections of a body of bone having a deficient portion. Then, plate members (i.e., a plurality o slices) made of wood are formed to have shapes corresponding to the body of bone of the cross sections, respectively.

15 By stacking the plate members, and adhering them together, a model correspor,ding to the entire body of bone having the deficient portion is formed.

Then, paper-mache pulp or the like is filled in the deficient portion of the model to obtain the shape of the bone 20 which should exist at the deficient portion. The model formed as above has stepped portions, at its side ends, corresponding to the thickness of the plate members.

Next, using resin material, the model is molded to form a female mold. Then, using the female mold, a male mold made of 25 resin is formed. Then, the steps at the side ends of the male

r mold are cut out using a cutter or the like so that the male mold has a smooth shape without stepped portions. The thus obtained smooth shape is regarded as the shape of the implant.

When the shape of the implant is determined in such a 5 manner, the following deficiencies are known to arise.

In the above-described method, the model is formed using plate members. Since each plate member is relatively thick, it is difficult to accurately form the model of the body of bone having the deficient portion.

10 Further, with the above method, the side end of the male mold is ground down using a cutter to obtain a smooth surface.

However, the actual shape of the body of bone at a surface where the bone is cut is not taken into consideration. Such an implant has less shape compatibility with respect to the body of bone.

15 If a thinner plate is used, it is possible to improve the shape compatibility of the model. However, there is a limitation to reducing the thickness of each plate member, and it would be difficult to obtain sufficient shape compatibility. Furthermore, if thinner plate members are used to form the model, it takes 20 a relatively long time for forming a model. Therefore, such a method cannot apply to a condition where the deficient condition cannot remain for a considerable period.

It is an object of the present invention to provide an improved method for forming an implant having an excellent 25 reproductivity of a missing portion of a bone.

It is a further objection of the present invention to provide a method for forming an implant which has an excellent shape suitability to a body of bone having a deficient portion.

According to one aspect Of the present invention there 5 is provided an implant designing method to be applied to a body of bone which has a bone deficient portion/ the bone being substantially symmetric with respect to a plane of symmetry. The method includes generating three-dimensiona' data of the bone based on a plurality of pieces of tomographic data of the bone, 10 and estimating a shape of a bore that is to exist at the bone deficient portion using part of the three-dimensional data corresponding to a symmetrical part of the bone deficient portion. since the missing portion to fit the deficient portion 15 is estimated based on the symmetrical part, an Replant having excellent shape suitability can be obtained.

In a particular case, the body of bone is a skull. Of course, the body of bone is not limited to the skulls but any bone can be subject to the method as far as it is symmetric with 20 respect to a certain plane.

According to an embodiment, a slicing interval of the tomographic data used for generating the three-dimensional data is within a range of 0.1 Gem through 5 mm.

According to another aspect, there is provided an implant forming method for forming an implant based on a design

r according to the above-described method, and further includes (a) forming a layer composed of an ingredient powder, and (b) hardening a reactant liquid by chemically reacting the ingredient powder with a reactant liquid in accordance with the 5 shape of the implant in accordance with the design. The forming and the making are repeated to stack a plurality of the layers to form an implant formed of the hardened portion of the layers of the ingredient powder.

Optionally, the porosity of the implant is within a range 10 of 10 vol% through 90 vol%.

According to a further aspect of the invention, there is provided an implant designing method to be applied to a bone body which has a bone deficient portion, the bone being in substantial symmetry with respect to a plane of symmetry, which 15 includes generating three-dimensional data of the bone body based on a plurality of pieces of tomographic data of the bone, and estimating a shape of the implant to be implanted at the bone deficient portion based on the three-dimensional data using a symmetric property of the bone body.

20 According to another aspect of the invention, there is provided an implant designing method to be applied to a bone body having a bone deficient portion, which includes generating three-dimensional data of the bone body, estimating the shape of an implant to be implanted to the bone deficient portion, and 25 modifying the three-dimensional data such that at least a part

- 6 of the implant in a circumferential direction has a shape that fits a corresponding portion of a bone cutting surface of the bone body.

According to this method, only with a slight processing 5 of the obtained implant, it fits the deficient portion.

Optionally, the estimating includes designing a shape of the implant that matches the shape of the outline of the bone cutting surface on the outer surface of the bone body, the implant having a substantially fixed shape in a direction of 10 thickness thereof, and the modifying includes overlapping the data representing at least the bone cutting surface of the bone body and the data of the implant, and eliminating data of the implant corresponding to a portion overlapping the bone body.

Still optionally, the step of estimating may include 15 generating outline data representing the outer surface of the implant so as to match with the shape of the outline of the bone cutting surface on the outer surface of the bone body, estimating the shape of the implant that has a predetermined thickness and a substantially fixed shape in the direction of 20 thickness, using the outline data, and eliminating, from the estimated shape data, data representing a portion overlapping the bone body so that the implant fits the shape of the bone cutting surface.

Alternatively, the step of estimating may include 25 generating outline data representing the outer surface of the

l implant so as to match with the shape of the outline of the bone cutting surface on the outer surface of the bone body, estimating the shape of the implant that has a predetermined thickness and a substantially fixed shape in the direction of 5 thickness, using the outline data, comparing data representing the shape of the implant which is generated in the estimating with at least part of the three- dimensional data representing the bone cutting surface, and compensating for the data representing the shape of the implant in accordance with a 10 comparison result of the comparing so that the implant fits the shape of the bone cutting surface.

Alternatively, the step of estimating may include generating outline data representing the outer surface of the implant so as to match with the shape of the outline of the bone 15 cutting surface on the outer surface of the bone body, estimating the shape of the implant that has a predetermined thickness and a substantially fixed shape in the direction of thickness, using the outline data, and eliminating, from the estimated shape data, data representing a portion overlapping 20 the bone body so that the implant fits the shape of the bone cutting surface.

Still alternatively, the step of estimating may further include generating outline data representing the outer surface of the implant so as to match with the shape of the outline of 25 the bone cutting surface on the outer surface of the bone body,

estimating the shape of the implant that has a predetermined thickness and a substantially fixed shape in the direction of thickness, using the outline data, comparing data representing the shape of the implant which is generated in the estimating 5 with at least part of the threedimensional data representing the bone cutting surface, and compensating for the data representing the shape of the implant in accordance with a comparison result of the comparing so that the implant fits the shape of the bone cutting surface.

10 In the above method, if the implant is applied to the bone deficient portion, the outer surface of the bone body and the outer surface of the implant come to substantially the same surface position.

Further optionally, the bone body is substantially 15 symmetrical with respect to a predetermined plane, a shape of an implant to be implanted at the bone deficient portion being estimated using shape data representative of a portion symmetrical to the bone deficient portion of the three-

dimensional data with respect to a substantial symmetry plane 20 of the three-dimensional data.

In a particular case, the body of bone includes a skull.

Optionally, a slicing interval of the topographic data to be used for generating the three-dimensional data is 0.1 mm through 5 mm.

25 According to another aspect of the invention, there is

9 - provided an implant forming method for forming an implant based on a design according to the above method, and further includes (a) forming a layer composed of an ingredient powder, and (b) hardening a reactant liquid by chemically reacting the 5 ingredient powder with a reactant liquid in accordance with the shape of the implant in accordance with the design. The forming and the making are repeated to stack a plurality of the layers to form an implant formed of the hardened portion of the layers of the ingredient powder.

10 Preferably, the porosity of the implant is within a range of 10 vol% through 90 vol%.

An example of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows an image of bones of skull generated in 15 accordance with three-dimensional data, which is generated based on a plurality of pieces of tomography data, the bone body having a portion of bone missing; Fig. 2 shows a cross-sectional view of an outer surface of a replacement or substitute portion, that corresponds to the 20 portion of bone which should exist at the missing portion, overlaid with the missing portion of the body of bone; Fig. 3 shows a cross-sectional view of the replacement portion, having a predetermined thickness overlaid with the missing portion of the body of bone; 25 Fig. 4 is a cross-sectional view of the replacement

portion, represented by replacement portion data, which is processed such that it matches the cut surface of the body of bone along the thickness direction thereof; Fig. 5 shows an implant manufacturing apparatus for 5 manufacturing an implant in accordance with a method according to an embodiment of the invention; Fig. 6 shows the implant manufacturing apparatus of fig. 5 when a first step of the manufacturing method is performed; Fig. 7 shows the implant manufacturing apparatus of fig. 10 5 when a second step of the manufacturing method is performed; Fig. 8 shows the implant manufacturing apparatus of fig. 5 when a third step of the manufacturing method is performed; Fig. 9 shows the implant manufacturing apparatus of fig. 5 after the first through third steps of the manufacturing 15 method have been performed; and Fig. 10 shows the implant obtained by repeating the first through third steps.

Hereinafter, a method of forming a three-dimensional implant according to an embodiment will be described with 20 reference to the accompanying drawings.

Fig. 1 shows an image of a body of bone (i.e., skull) generated in accordance with three-dimensional data, which is generated based on a plurality of pieces of tomography data, the bone body having a portion of bone missing. Fig. 2 is a drawing 25 showing a condition where data for the outer surface shape of

a replacement or substituted bone portion, that corresponds to the bone that should exist at the missing portion, is overlapped with the actual missing portion. Fig. 3 is a drawing showing a condition where data for the replacement bone portion having 5 a predetermined thickness is overlapped with the missing portion, and Fig. 4 is a drawing showing data for the replacement bone portion that has been processed so as to match with the cut surface of the missing portion throughout the entirety in the direction of thickness of the bone. In Fig. 2 10 through Fig. 4, the upper edge shows the outer surface side of the bone three-dimensional data, and the lower edge shows the inner surface side of the bone three- dimensional data.

With one aspect of the embodiment, a replacement bone portion corresponding to the missing portion of the body of bone 15 is estimated using a symmetric property of the body of bone. It should be noted that the body of bone for which an implant is formed may be any type of body of bone if it is substantially symmetrical with respect to a certain plane.

With another aspect, the replacement bone portion is 20 formed so as to fit onto a cut surface of the missing portion.

For this purpose, the body of bone for which an implant is formed may be any type of body of bone.

Examples of such a body of bone include the skull, cheekbone and jaw bone. In the description below, the skull

25 bones used as the body of bone are substantially symmetrical

- 12 with respect to a certain plane, having a deficient portion.

Data of Three-Dimensional Structure Firstly, data 100 (hereinafter referred to as three-

dimensional data 100) representing a three-dimensional structure 5 of the bone having a missing portion of bone lbl as shown in Fig. 1 is prepared. The three-dimensional data 100 is prepared based on a plurality of pieces of tomographic data corresponding to a plurality of slices, respectively. As tomographic data, for example, a CT film and CT data (data outputted from a CT device) 10 can be used.

By organizing the plurality of pieces of tomographic data so as to represent stacked slices of the body of bone, the three-dimensional data 100 can be obtained.

A slicing interval of the tomographic data (distance 15 between adjacent pieces of tomographic data) is not limited to a particular value, however, it is preferably 0.1 mm through 5 mm, and more preferably 0.3 mm through 3 mm.

If the slicing interval is less than the lower limit, depending on the size of the implant, the required number of 20 pieces of tomographic data becomes excessively large. In such a case, the time required for preparing the three-dimensional data 100 is extended, and the accuracy of the three-dimensional data 100 substantially levels off. Accordingly, at the present time, it becomes difficult to further improve the dimensional 25 accuracy of the implant.

- 13 If the slicing interval exceeds the upper limit, the accuracy of the three-dimensional data 100 may become insufficient. It is preferable that the three-dimensional data 100 is 5 obtained by layering a plurality of pieces of tomographic data and further smoothing the surface. Thereby, reproducibility of the implant is significantly improved.

Estimate of Share of Missing Portion Based on the three-dimensional data 100 thus obtained, 10 the shape of the bone that should exist at the missing portion 101 is estimated, and the shape of a replacement bone portion is obtained as three-dimensional data (hereinafter referred to as replacement portion data 13).

Estimate of Outer Surface of Missing Portion 15 The replacement portion data 13 can be obtained by the following method.

To obtain the replacement portion data 13, first, based on the threedimensional data 100 that has been obtained as mentioned above, outline data 131 representative of the outer 20 surface of a body of bone that should exist at the missing portion 101 (i.e., the deficient portion) is obtained.

For the outline data 131, outline data representing the outer surface side of a cut surface 104 represented by the three-dimensional data 100 can be used as it is. However, if the 25 three-dimensional data 100 represents a bone substantially

- 14 symmetrical with respect to a certain plane, it is preferable that the outline data is obtained by the following method.

First, the body of bone represented by the three-

dimensional data 100 is divided at a plane 102 of substantial 5 symmetry. The plane 102 is a plane perpendicular to the plane of the sheet of Fig. 1. With respect to the plane 102, the body of bone is divided into a half section 11 which has the bone deficient portion 101 and a half section 12 which does not have the bone deficient portion 101 are supposed.

10 Next, at least a part of the outer surface shape data of the half section 12 is inverted, with respect to the symmetry plane 102, to the half section 11 side. It should be noted that the outer surface shape data of the half section 12 to be inverted is only required to include the shape data of a portion 15 103, which is symmetrical to the missing portion 101 with respect to the symmetry plane 102.

When the outer surface shape data of the half section 12 is inverted, a portion which overlaps the inverted shape is a part of the non-deficient portion 105. Therefore, in the outer 20 surface shape data representing the inverted half section 12, only a portion that does not overlap the outer surface shape of the half section 11 is extracted, whereby the outer surface shape (outer surface shape data 132) of the implant to be applied to the missing portion 101 can be determined (see Fig. 25 2). The outline 132 of the outer surface shape data thus

- 15 obtained represents the outline 131 which is required to be determined. By determining the outline 131 as described above, even if, for example, the shape of the outline at the outer surface 5 side of the cut surface 104 is not clear, sufficiently accurate outline data 131 can be obtained.

Further, if such a method is used, as described above, shape data (outer surface shape data 132) of the entire outer surface of the replacement portion that is to correspond to the 10 bone that is to exist at the missing portion 101 is obtained along with the outline 131. Since the outer surface shape 132 is obtained as described above, it is possible to estimate even a complicated shape including minute unevenness that the bone originally has. As a result, the implant to be designed becomes 15 excellent, particularly in shape suitability to the bone.

In the above-mentioned method, since the outer surface shape of the replacement portion that corresponds to the bone that should exist at the missing portion 101 is estimated using shape data of a part of the bone (shape data representing the 20 outer surface shape of the portion 103 symmetrically corresponding to the missing portion 101), shape suitability to the bone becomes excellent even when the implant to be designed is comparatively large.

Data representing the outer surface shape 132 thus 25 estimated is preferably at the same surface position as that of

- 16 the outer surface of the body of bone represented by the three dimensional data 100. Thereby, the finally obtained implant becomes excellent particularly in shape suitability to the bone.

In the method described above, the outline data 131 and 5 the outer surface shape data 132 are obtained simultaneously.

However, these pieces of data may be separately obtained. For example, the outer surface shape data 132 can be determined after the outline data 131 is obtained.

Estimate of the Thickness of Implant 10 Using the outer surface shape data 132 estimated as described above, the shape of the implant having a predetermined thickness is estimated, and the replacement portion data 13 is obtained. Normally, the thickness of the implant is estimated based on the thickness of the non-deficient portion 105.

15 Generally, the side surface of the obtained replacement portion data 13 (surface that should come into contact with the cut surface 104) is substantially flat and smooth without unevenness along the thickness direction.

It should be noted that the replacement portion data 13 20 may be any type as long as the data is three-dimensional data which is a group of points, lines, plane data or the like.

Estimate of Shape of Contact Surface Generally, the cut surface of a body of bone having a missing portion is minutely uneven, and does not have a fixed 25 shape along the direction of thickness thereof. Typically, the

l - 17 area of the missing portion tends to be larger at the outer surface side thereof, and smaller at the inner surface side.

This is because when an implant is to be put at the missing portion, in order to prevent the implant from sinking inward, 5 the body of bone is cut such that the outer area is greater and the inner area is smaller.

Therefore, when the replacement portion data 13, obtained as described above, is overlapped with the bone deficient portion 101 of the threedimensional data 100, a part of the 10 replacement portion data 13 overlaps the non-deficient portion 105 of the three-dimensional data 100. The overlapped portion defines an overlapping portion 133 (a roughly triangular section shown by the lattice pattern in Fig.3). If this overlapping portion 133 is kept, the designed implant does not match the cut 15 surface 104 when applied to the body of bone having the missing portion. Therefore, with the present embodiment, the replacement portion data 13 is corrected so as to fit the shape of the cut surface 104 so that the replacement portion data 13 does not 20 overlap the three- dimensional data 100. With this correction, it is ensured that the finally obtained implant fits the bone cutting surface of the body of bone.

Such a correction is carried out by eliminating the data corresponding to the overlapping portion 133 from the 25 replacement portion data 13. That is, part of the replacement

- 18 portion data 13 at portions where the replacement portion data 13 and non-deficient portion 105 overlap each other when the outer surface shape data 132 matches the outline of the outer surface side of the cut surface 104, is eliminated (see Fig. 4).

5 As a result, an implant that is formed based on the replacement portion data 13 thus corrected corresponds well with the shape of the cut surface of the body of bone, and the implant becomes excellent in stability when it is applied to the bone. 10 Furthermore, with the present embodiment, the implant is designed so as to match the shape of the cut surface of the body of bone, and therefore, trimming that has been conventionally applied to an implant during an operation can be omitted or simplified. As a result, it becomes possible to shorten the 15 operation time, and also to reduce the burden on a patient.

The replacement portion data 13 obtained as described above can be used as implant shape data as it is. Optionally, the data may be further corrected as necessary. A correction to be applied to the replacement portion data 13 may include a 20 change of the curvature, thickness and the like of at least a part of the implant. With such a correction, the finally obtained implant becomes excellent in shape suitability to the bone, and the stability of the finally obtained implant is further improved.

- 19 Implant Forming Method Next, an implant forming method will be described. An implant is formed based on the above-described design data. It should be noted that, when an implant is formed, shape data 5 obtained by the above-described designing method may be subjected to various processing such as rotation processing.

Hereinafter, the implant forming method will be described in detail.

Figs. 5 through 9 show cross-sectional views of an 10 implant forming apparatus 1 at various stages of an implant forming method in accordance with an embodiment of the invention. Fig. 10 shows an example of an implant formed by this method. As shown in Fig. 5, the implant forming apparatus 1 has 15 an ingredient supplying tank 2, an implant forming stage 3, a roller 4 and a liquid supplying head 5. It should be noted that the implant forming apparatus 1 has a certain width in a direction perpendicular to a surface of the drawing.

In the ingredient tank 2, powdered ingredient material 20 6 used for forming an implant 9 is stored. A bottom of the ingredient supplying tank 2 has a piston structure 21, which is movable in a vertical direction (i. e., in an up-down direction in Fig. 5). Since various such mechanisms are known, and any of such mechanisms can apply to the implant forming apparatus 25 the piston mechanism will not be described in detail.

- 20 The ingredient material is carried from the ingredient supplying tank 2 to the implant forming stage 3, on which the ingredient material 6 is reacted with reactant liquid 7 to form the implant (see Fig. 7). The implant forming stage 3 is also 5 provided with a piston mechanism 31, movable in the vertical direction (i.e., in the up-down direction in Fig. 5).

The roller 4 is supported by a supporting device 10 so as to rotatable about a shaft 41 that is held in the supporting device 10. The supporting device 10 is movable in a forwards and 10 backwards horizontal direction (i.e., in the right and left hand direction in Fig. 5). As the supporting device 10 moves in the forward horizontal direction, the roller rotates and moves onto the ingredient supplying tank 2 and the implant forming stage 3. As will be described in detail below, as the roller moves, 15 some of the powered ingredient material 6 is carried onto the implant forming stage 3 to form an ingredient layer 61 of the ingredient material on the implant forming stage 3.

The liquid supplying head 5 is held by the supporting device 10 and is configured to deposit or blow out the reactant 20 liquid 7 toward at least a part of the ingredient layer 61 on the implant forming stage 3.

A method for forming the implant using the above described implant formingapparatus 1 will be described in detail with reference to Figs. 6 through 8.

25 The method includes the steps of:

- 21 (a) forming a layer of powdered ingredient on the implant forming stage; (b) blowing out the reactant liquid onto at least a part of the layer of the powered ingredient; and 5 (c) moving the implant forming stage downward, and repeating steps (a) and (b).

Each step will be described in detail hereinafter.

As shown in Fig. 5, when the powdered ingredient slightly protrudes with respect to the plane of a top surface 10 of the apparatus 1 on which the roller 4 contacts, the supporting device 10 is moved to pass over the ingredient supplying tank 2 and the implant forming stage 3 (i.e., the supporting device 10 moves forward from the left hand side of the ingredient supplying tank 2 to the right hand side end of 15 the implant forming stage 3. Fig. 6 shows a state when the above movement has finished.

With this movement, the roller 4 moves, whilst rotating about the shaft 41, and carries or pushes the protruded portion of the powdered ingredient of the ingredient supplying tank 2 20 onto the implant forming stage 3 to form the layer 61.

The mean thickness of the layer 61 is not limited to a specific value, and is determined based on characteristics of the powdered ingredient and the reactant liquid. Generally, the mean thickness may be in a range of 0. 1 mm through 0.5 mm.

25 Preferably, the mean thickness is in a range of 0.1 mm through

- 22 0.3 mm.

If the mean thickness is too small, dispersion of the thickness of the layer 61 tends to increase. Further, if an implant 9 to be formed is relatively large in size, the time 5 period for forming the entire implant may become long, which lowers productivity for the implants.

If the mean thickness is too large, the reactant liquid 7 may not cause sufficient reaction, and the mechanical strength of the resultant implant may not be sufficient. Further, the 10 accuracy in size tends to be lowered.

It should be noted that residual powdered ingredient, which is carried from the ingredient supplying tank 2 and does not contribute to form the layer 61 is collected by an ingredient collection tank 8.

15 Next, as the device 10 moves in a reverse direction, the reactant liquid 7 is applied to a portion of the layer 61 formed on the implant forming stage 3. Thus, a chemical reaction is induced between the powdered ingredient layer 61 and the reactant liquid 7, whereby the powdered ingredient material 6 20 in the layer is hardened to form a hardened section 62.

It should be noted that, with the present embodiment, the ingredient material 6 is hardened by the chemical reaction between the ingredient material 6 and the reactant liquid 7.

That is, the powdered ingredient material 6 can be hardened 25 without addition of a binding agent. Therefore, it is possible

- 23 to form an implant including less impurities. Such an implant has an excellent biocompatibility to living body.

With the embodiment, the reactant liquid 7 is supplied from the supplying head 5 as drops of liquid. Since the reactant 5 liquid 7 is supplied as described above, the reactant liquid 7 can be efficiently supplied with a high accuracy to designated portion of the powdered ingredient material 6. As a result, the accuracy in size of the finished implant can be improved, and the productivity thereof is also improved.

10 As shown in Fig. 7, for the step of supplying the reactant liquid 7, the supplying head 5 moves across the implant forming stage 3 and the ingredient supplying tank 2 in the substantially horizontal reverse direction, and supplies the drops of reactant liquid 7 so that portions corresponding to a 15 desired pattern are formed as the hardened section 62. The desired pattern is generally determined based on the data extracted from the CT film and the like i.e. the replacement portion data. If it is known that the hardened section 62 shrinks during the following process, the pattern is determined 20 taking the shrinking effect into account.

Next, by operating the piston structure 21 the bottom plate of the ingredient supplying tank 2 can be moved upward to change the position of the upper surface of the powdered ingredient material 6 (i.e., the protruded amount thereof). At 25 the same time, the piston structure 31 is operated to lower the

- 24 -

lmplant forming stage 3 to change the position of the upper surface of the layer 61 (i.e., the height of the layer 61 formed by the successively supplied ingredient material). The moving amount of the piston 21 preferably corresponds to the amount of 5 ingredient material supplied from the ingredient supplying tank 2 to the implant forming stage 3 at the first step above.

Further, the moving amount of the piston 31 is preferably the same as the average thickness of the layer 61 formed in the first step. With the above configuration, the thickness of each 10 of the layers 61 is maintained substantially constant.

Repeating the first through third steps, a plurality of layers 61 are successively formed or layered as shown in Fig. 9, and the hardened portion 62 forms a desired implant shape.

As described above, by stacking the hardened portion 62 15 of each layer 61, the implant 9 is formed. According to this process, even if the implant 9 has a relatively complicated shape, it can easily be formed. Further, the obtained implant 9 has excellent dimensional accuracy. Furthermore, according to this process, a desired implant 9 can be formed within a 20 relatively short period of time. Therefore, the implant 9 can be formed even when an emergency operation is to be performed.

After the implant forming process is completed, the implant forming stage 3 is lifted and unhardened powdered ingredient material 6 is removed, whereby the implant 9 having 25 the desired shape is obtained. The unhardened ingredient

- 25 material 6 may be removed easily, for example, by blowing air thereat. The implant 9 thus obtained may be subject to treatment such as sistering or impregnation with a chemical agent (a bone 5 morphogenic agent such as BMP or TGF, or a bone inducer such as PG) as necessary.

It is preferable that the implant 9 thus obtained has an appropriate porosity so that when the implant 9 is implanted in a living body, osteoblast easily invades in the pores of the 10 implant 9, and bone formation proceeds smoothly. As a result, the period can be shortened for the implant 9 to become stable.

The porosity of the implant 9 is, for example, preferably 10 through 90 vol%, and more preferably 30 through 80 vol%.

If the porosity of the implant 9 is too small, the 15 osteablast may not invade in the pores of the implant 9 sufficiently, and bone formation does not proceed well.

If the porosity of the implant 9 is too large, a sufficient mechanical strength of the implant 9 may not be obtained. 20 The pores formed in the implant 9 are preferably continuous pores, whose mean diameter is 100,um or more. If the pore diameter is less than 100 um, the osteablast does not invade in the pores of the implant 9 sufficiently, and bone formation may not proceed well. If the pore diameter is too 25 large, however, sufficient mechanical strength of the implant

9 may not be obtained.

As described above, the powdered ingredient material 6 is hardened by chemical reaction between the ingredient material 6 and the reactant liquid 7 Therefore, the ingredient material 5 6 can be hardened without adding a binder. Accordingly, the implant 9 includes less impurities, and thus, it has excellent biocompatibility. Further, both the ingredient material 6 and reactant liquid 7 may have excellent biocompatibility. In such a case, 10 even when the ingredient material 6 and reactant liquid 7 remain unreacted, a harmful influence on the living body can be prevented effectively.

Hereinafter, the ingredient material 6 and the reactant liquid 7 will be described in detail.

15 Ingredient Material As the ingredient material 6, a powder which contains -

tricalcium phosphate, tetracalcium phosphate, and calcium hydrogenphosphate is used.

The -tricalcium phosphate and tetracalcium phosphate to 20 be used may be separately produced by well-known methods, or a mixture of -tricalcium phosphate and tetracalcium phosphate which are obtained by sistering hydroxy apatite can be used.

When the hydroxy apatite is sintered, the sistering condition should be 1150 C through 1450 C for about one hour 25 under decompression.

- 27 The calcium hydrogen phosphate may also be one manufactured by a well-known method, and either anhydride (CaHPO4) or hydrate (for example, dihydrate (CaHPO4 2H2O), etc.) may be used.

5 The ingredient material 6 may further contain, as appropriate, hydroxy apatite, fluoroapatite, p-tricalcium phosphate, and calcium pyrophosphate in addition to the abovementioned three substances.

The ingredient material 6 for this embodiment chemically 10 reacts with the reactant liquid 7 and is hardened.

The Ca/P ratio of the ingredient material 6 is 1.40 through 1.80, and is preferably 1.40 through 1.67. If the Ca/P ratio is less than 1.40 or exceeds 1.80, the hardening reaction does not proceed at a sufficient reaction rate, and the 15 mechanical strength of the obtained implant 9 may be less than required. In the ingredient material 6, additives such as an X ray contrast medium, an antibacterial agent, a bone morphogenic factor such as BMP or TGF and a bone inducer such as PG may be 20 added as necessary. The X ray contrast medium is not especially limited, and various X ray contrast media can be used, for example, one or more kinds among barium sulphate, basic bismuth carbonate, and iodoform can be used. As an antibacterial agent, iodoform and chlorhexidine or the like, can be used.

25 The mean particle size of the powdered ingredient

- 28 material 6 is preferably 10 Am through 100,um, and more preferably 20 Am through 40,um.

If the mean particle size of the powdered ingredient material 6 is less than the lower limit (i.e., 10 up), it 5 becomes difficult to handle the ingredient material 6. Also, if the average particle size of the ingredient material 6 is less than the lower limit, the porosity of the obtained implant 6 becomes too low, and the bone formation may not proceed well.

If the mean particle size of the ingredient powder 6 10 exceeds the upper limit, depending on the size of the implant 9 to be formed by the abovementioned forming process, sufficient dimensional accuracy may not be achieved.

Reactant Liquid Any type of reactant liquid 7 can be used if it 15 chemically reacts with the ingredient material 6 and hardens it. Preferably, the reactant liquid is water or liquid mainly composed of water.

If such a reactant liquid 7 is used, the hardened portion 62 formed by reaction between the ingredient material 6 and the 20 reactant liquid 7 has a superior mechanical strength. In particular, if water or a liquid mainly composed of water is used as the reactant liquid 7, apatite (hydroxy apatite or octacalcium phosphate) is produced by reaction with the ingredient material 6. It is known that the apatite has 25 excellent biocompatibility. Therefore, a high-specification

- 29 implant 9 can be provided.

In the reactant liquid 7, as components other than water, various preparations may be included, for example, organic acids such as acetic acid, lactic acid, citric acid, malic acid, 5 malonic acid, succinic acid, glutaric acid, tartaric acid, polyacrylic acid, and gluconic acid or the like, inorganic acids such as phosphoric acid, a pH regulator, a thickener, an x ray contrast medium, an antibacterial agent, a bone morphogenic factor such as BMP or TGF, and a bone inducer such as PG may be 10 contained.

The reaction liquid 7 may contain insoluble substances if they have sufficient fluidity.

As in the above, an implant forming method and an implant according to the exemplary embodiment have been described, 15 however, the invention is not limited to the described one.

For example, in the above-mentioned embodiment, an implant and an implant designing method which are applied to the cranium have been described, however, the implant can be applied to various bones.

20 Furthermore, in the embodiment, it has been described that the reaction liquid hardens the ingredient material by chemically reacting therewith, however, the invention is not limited to such a configuration. Namely, any reactant liquid can be used if the liquid hardens the ingredient material. For 25 example, as in the case of a liquid containing methyl cellulose

- 30 -

and polyvinyl alcohol, any liquid (binder) which hardens the ingredient material without a chemical reaction can be used.

A light sensitive binder could be employed.

As mentioned above, with the present invention, an 5 implant which is excellent in reproducibility and/or shape suitability of a bone deficient portion can be provided.

In addition, even when an implant to be formed is relatively large, an implant with excellent reproducibility and/or shape suitability can be provided.

10 Conventionally' it has been extremely difficult to estimate the shape of a bone that should exist at a missing portion, if the body of bone is a cheekbone or jawbone. With the above-described embodiment, even in such a case, an implant with excellent reproducibility can be provided.

Claims

l - 31 CLAIMS:

1. An implant designing method to be applied to a body of bone which has a portion of bone missing, the bone being in 5 substantial symmetry with respect to a plane of symmetry, the method comprising: generating threedimensional data of the bone based on a plurality of pieces of tomographic data of the bone; and estimating a shape of the bone, which should exist at the 10 missing portion, using part of the three- dimensional data corresponding to a symmetrical part of the missing portion.

2. An implant designing method according to claim 1, wherein the bone body is a skull.

3. An implant designing method according to claim 1 or 2, 15 wherein a slicing interval of the tomographic data used for generating the threedimensional data is within a range of 0.1 mm through 5 mm.

4. An implant designing method to be applied to a body of bone which has a portion of bone missing, the bone being in 20 substantial symmetry with respect to a plane of symmetry, the method comprising: generating threedimensional data of the bone body based on a plurality of pieces of tomographic data of the bone; and estimating a shape of the implant to be implanted at the 25 missing portion based on the three-dimensional data using a

- 32 symmetric property of the bone body.

5. An implant designing method to be applied to a body of bone having a missing bone deficient portion, the method comprising: 5 generating threedimensional data of the bone body; estimating the shape of an implant to be implanted at the missing portion; and modifying the three-dimensional data such that at least a part of the implant in a circumferential direction has a shape 10 that fits a corresponding portion of a cut surface of the bone body.

6. An implant designing method according to claim 5, wherein the estimating includes designing a shape of the implant that matches the shape of the outline of the cut surface on the outer 15 surface of the bone body, the implant having a substantially fixed shape in a direction of thickness thereof, and wherein the modifying includes overlapping the data representing at least the cut surface of the bone body and the data of the implant, and eliminating data of the implant 20 corresponding to a portion overlapping the bone body.

7. An implant designing method according to claim 5 or 6, wherein the estimating includes: generating outline data representing the outer surface of the implant so as to match with the shape of the outline of 25 the cut surface on the outer surface of the bone body;

- 33 -

estimating the shape of the implant that has a predetermined thickness and a substantially fixed shape in the direction of thickness, using the outline data; and eliminating from the estimated shape data, that data 5 representing a portion overlapping the bone body so that the implant fits the shape of the cut surface.

8. An implant designing method according to any one of claims 5 to 7, wherein the estimating includes: generating outline data representing the outer surface 10 of the implant so as to match with the shape of the outline of the cut surface on the outer surface of the bone bodyi estimating the shape of the implant that has a predetermined thickness and a substantially fixed shape in the direction of thickness, using the outline datai 15 comparing data representing the shape of the implant which is generated in the estimating with at least part of the threedimensional data representing the cut surfaces and compensating for the data representing the shape of the implant in accordance with a comparison result of the comparing 20 so that the implant fits the shape of the cut surface.

9. An implant designing method according to any of claims 5 to 8, wherein if the implant is applied to the missing portion, the outer surface of the bone body and the outer surface of the implant come to substantially the same surface 25 position.

! - 34

10. An implant designing method according to any one of claims 5 to 9, wherein the bone body is substantially symmetrical with respect to a predetermined plane, a shape of an implant to be implanted at the missing portion being 5 estimated using shape data representative of a portion symmetrical to the missing portion of the three-dimensional data with respect to a substantial symmetry plane of the three-

dimensional data.

11. An implant designing method according to any of claims 10 5 to 10, wherein the bone is the cranium.

12. An implant designing method according to any one of claims 5 to 11, wherein a slicing interval of the topographic data to be used for generating the three-dimensional data is 0.1 mm through 5 mm.

15

13. An implant designing method to be applied to a body of bone which has a portion of bone missing, the bone being in substantial symmetry with respect to a plane of symmetry, the method comprising: substantially as herein described with reference to the 20 accompanying drawings.

14. An implant that is formed based on a designing method according to any preceding claim.

15. An implant forming method for forming an implant based on a design method according to one of claims 1 to 13, the 25 method including:

- 35 (a) forming a layer composed of a powdered ingredient material; and (b) applying a reactant liquid to the layer of powdered ingredient material for hardening the ingredient material and 5 in accordance with the shape of the implant in accordance with the design, wherein steps (a) and (b) are repeated to stack a plurality of layers to produce an implant formed of the hardened portion of the layers of the ingredient material.

10

16. An implant which is formed in accordance with the implant forming method of claim 15.

17. An implant according to claim 15 or 16, wherein the porosity of the implant is within a range of 10 vol% through 90 vol%.